Liquid crystal display elements, utilizing characteristics of liquid crystal compounds such as optical (refractive index) anisotropy (Δn; hereinafter, may simply be referred to as Δn) and dielectric anisotropy (Δ∈; hereinafter, may simply be referred to as Δ∈), have been manufactured in large quantities and are used for watches, clocks, electronic calculators, various measuring instruments, automotive instrument panels, word processors, electronic notebooks, portable telephones, printers, computers, television sets, and the like with demand increasing year by year. A liquid crystal compound has a specific liquid crystal phase between a solid phase and a liquid phase. The liquid crystal phase is classified broadly into nematic, smectic, and cholesteric phases, of which nematic phase is, at present, most widely used for liquid crystal display elements.
With regard to display and driving methods applied to liquid crystal displays, many modes have been devised. As display modes, there are known, for example, dynamic scattering (DS), guest-host (GH), twist nematic (TN), super twist nematic (STN), thin-film transistor (TFT), ferroelectric liquid crystal (FLC), polymer dispersed liquid crystal (PDLC) modes, and the like. As driving modes, there are known static, time-division, active matrix, dual frequency modes, and the like. Especially in the active matrix driving mode, the liquid crystal material is generally required to have high stability toward heat and light, and thus fluorinated compounds with superior stability are used as liquid crystal materials.
Liquid crystal display elements are required to exhibit various performances such as a wide operation temperature range, low operating voltage, fast response, high contrast ratio, wide viewing angle, chemical stability, and the like. At present, however, there is no material which can satisfy all these characteristics by itself. Therefore, a liquid crystal material and a non-liquid crystal material, each having one or more superior characteristics, are mixed together to provide a liquid crystal composition, wherein the components supplement each other to satisfy the various requirements. Thus, in developing a liquid-crystal or non-liquid crystal material, efforts are generally made to develop one which is excellent in one or more characteristics, not in all of them.
The performance items required for liquid-crystal display elements are low-power driving and fast response in battery-driven elements, high resolution and fast response in OA instruments, low-temperature response or fast response over a wide operation temperature range in displays for automobile, and the like. Thus, improvement in response speed is especially desired.
The response speed (τ) is known to be proportional to the product of viscosity (η) of the liquid crystal material and square of the cell thickness (d). Namely, the following equation holds.τ∝ηd2 
Accordingly, fast response is achieved when a low-viscosity liquid crystal material is used and the cell thickness decreased. Especially, the effect of decrease in the cell thickness (d) is large. In decreasing the cell thickness, it is necessary to set the value of retardation [product of optical (refractive index) anisotropy (Δn) of the liquid crystal material and cell thickness (d)] within a certain range, the retardation being related to the contrast ratio of the liquid crystal display element. Thus, to decrease the cell thickness, a liquid crystal material with large Δn becomes necessary. Namely, in order to achieve fast response, development of a liquid crystal material of low-viscosity and large Δn is desired.
Further, the threshold voltage of a field effect-type liquid crystal display device, which uses a liquid crystal composition of positive dielectric anisotropy (Δ∈), is generally known to be in reverse proportion to the square root of Δ∈ of the composition. In recent years, in twist nematic (TN) liquid crystal elements, battery-driven types have become the main stream and liquid crystal materials, especially, of low threshold voltage are desired. For this purpose, liquid crystal materials with large and positive Δ∈ are important.
Furthermore, low-temperature storage stability of a liquid-crystal material is usually evaluated from a standpoint of the lowest temperature at which the liquid crystal phase is exhibited. Thus, the lower that value is, the lower the temperature is at which the liquid crystal phase is exhibited. Especially when liquid crystal materials are used in cold regions, low-temperature storage stability is required.
Compounds having fluoroalkyl(oxy) end groups show positive dielectric anisotropy and are known as liquid crystal materials which exhibit high resistivity, high voltage holding ratio (VHR), low ionic density, and the like, which are required especially in the active matrix driving mode. Thus, attempts have been made to introduce a fluoroalkyl(oxy) group to compounds. For example, various compounds having fluoroalkyl groups are proposed in Patent Documents 1 to 9 and others. Also, in Patent Document 10 there is proposed an electro-optical display element utilizing a compound having a fluoroalkyl group and, further, in Patent Documents 11, and 12, and others there are proposed active matrix liquid crystal display elements using compounds having fluoroalkyl(oxy) groups, and others.
The present applicant proposed a compound having a fluoroallyloxy end group in Patent Document 13. The compound is a liquid crystal material having characteristics with low viscosity and high dielectric anisotropy (Δ∈).    Patent Document 1: Japanese Patent Laid-Open Publication No. S55-72143    Patent Document 2: Japanese Patent Laid-Open Publication No. S55-40660    Patent Document 3: Japanese Patent Laid-Open Publication No. S61-197563    Patent Document 4: Japanese Patent Laid-Open Publication No. S56-12322    Patent Document 5: Japanese Patent Laid-Open Publication No. S58-154532    Patent Document 6: Japanese Patent Laid-Open Publication No. S58-177939    Patent Document 7: Japanese Patent Laid-Open Publication No. S58-210045    Patent Document 8: Japanese Patent Laid-Open Publication No. S59-78129    Patent Document 9: Japanese Patent Application Laid-Open No. H6-500343    Patent Document 10: Japanese Patent Application Laid-Open No. H1-503145    Patent Document 11: Japanese Patent Application Laid-Open No. H3-502942    Patent Document 12: Japanese Patent Laid-Open Publication No. H10-67989    Patent Document 13: International Publication No. WO2004/058676